Soil contamination is caused by the presence of non-naturally occurring substances in the natural soil environment. The contamination can be caused by any number of things, for example, leakage from underground storage tanks, usage of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of water from landfills or direct discharge of industrial wastes to the soil. The most common substances found to contaminate soil include petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. Soil contamination presents health risks from the contact with the contaminated soil and contaminant vapors and from contamination of water supplies within the soil. Soil contamination may also have detrimental effects on ecosystems and agricultural lands. For at least these reasons, soil decontamination becomes necessary.